Deep sea organisms

Marine Biology Overview

  • Focus on mesopelagic and bathypelagic zones.

  • Study of adaptations and biodiversity in ocean's depths.

Lecture Content

  • Topics:

    • Conditions driving adaptation in mesopelagic and bathypelagic environments.

    • The unique adaptations of species in these zones.

    • Overview of pelagic biodiversity.

Oceanic Zones

Key Characteristics

  • Mesopelagic Zone (200-1000m):

    • Short wavelength (blue) light dominance.

    • Lack of primary productivity.

    • Oxygen concentration varies; can be anoxic in Oxygen Minimum Zones (OMZs).

    • Temperature drops (~5°C) with depth.

    • Decrease in zooplankton biomass.

    • Gradual salinity and pressure increase (20-100 atm).

    • High amounts of Dissolved Organic Matter (DOM) and Particulate Organic Matter (POM).

    • Demonstrates Diurnal Vertical Migration (DVM).

  • Bathypelagic Zone (>1000m):

    • Bioluminescence is the only light source (typically blue/green).

    • No primary productivity or significant photosynthetic activity.

    • Abundant oxygen levels.

    • Constant low temperature (1-4°C).

    • Gradual salinity increase with depth.

    • Extremely high pressure (>100 atm).

    • Food is limited.

Energetic Adaptations

Management Strategies

  • Meso- and bathypelagic species have developed three energy management strategies:

    • Efficient consumption of food resources.

    • Adaptations for efficient digestion and metabolic conversion.

    • Reduction of energy expenditure to survive in low-resource environments.

Feeding Strategies

  • Transition from filter feeding to carnivory at greater depths.

  • Adoption of "lurk and lure" strategies for food capture.

Examples in Fish

  • Development of lures.

  • Enlarged sensory appendages for prey detection.

  • Ability to consume larger prey items due to enlarged teeth and flexible jaw articulations.

  • Predominantly generalist feeders capable of stomach distension.

Examples in Invertebrates

  • Ability to consume large food quantities when available.

  • Considered generalist scavengers; capable of sustaining on one meal for a year.

  • Possess elastic stomachs for food storage.

Metabolism in Deep-sea Species

  • Many pelagic species exhibit reduced metabolism with increasing depth, adapting to:

    • Lower food availability.

    • High-pressure environments.

    • Low light levels, reducing predatory pressures.

Buoyancy Adaptations

  • Evolution favors reduced density to prevent sinking.

Mechanisms to Achieve Buoyancy

  • Increased water or jelly content (e.g., in ctenophores, salps).

  • Accumulation of light ions (e.g., Na+, NH4+, Cl-).

  • High lipid content (triglycerides and wax esters).

  • Reduction in skeletal density; loss of swim bladders in some species.

Pressure Adaptations

  • Deep-sea species possess:

    • Enzymes tolerant to high pressures but exhibit lower catalytic efficiency.

    • Homeoviscous adaptations in cell membranes (greater proportions of unsaturated fatty acids).

Vision Adaptations

Eye Structure and Function

  • Many mesopelagic fish possess tubular eyes for enhanced prey detection.

  • Large aperture lenses focusing light on small retina areas; typically no cones.

  • Multi-bank retinas for increased sensitivity in low light.

  • Tapetum reflects light back into retina, sensitive to short wavelengths (485 nm).

Eye Adaptations

  • Some species have an aphakic gap to maximize light capture.

  • Sensitivity to red wavelengths varies among species; some use yellow lenses to detect bioluminescence.

Chemoreception in Deep Sea

  • Critical for food detection in low-light, low-biomass environments.

  • Rapid responses to food falls from above; can locate food within 30-40 minutes.

Pheromones and Communication

  • Important for conspecific interactions; may show sexual dimorphism in olfactory structures.

  • Olfactory adaptations differ based on habitat preferences.

Camouflage Mechanisms

Transparency

  • Many pelagic invertebrates are transparent for camouflage.

  • Effective at depth due to similar refractive indices to water.

Silvering and Countershading

  • Silvering employs guanine panels for concealment.

  • Bioluminescence used for countershading; ventral surfaces adapted for survival.

Bioluminescence Mechanisms

Overview

  • Bioluminescence involves luciferin and luciferase; can be self-generated or symbiotic.

Light Organs

  • Found in various fish types, with specialized conditions for operation.

  • Symbiotic relationships with bioluminescent bacteria aid in light production.

Functions

  • Locating food, attracting mates, and evading predators are key roles of bioluminescence.

  • Utilizes a variety of strategies to maximize effectiveness and minimize detection.

Red Bioluminescence

  • Specific fishes like Malacosteus exhibit red bioluminescence, particularly in deeper environments.

  • Red light perception aids in prey location, particularly copepod species.